Tractors, and trailers designed to be pulled by them, have been in use almost as long as automotive vehicles. They are used to move many different types of loads, including cargoes, machinery, tools, and devices for supplying electric, pneumatic, or hydraulic power. Although tractors are often used to pull wheeled trailers, sometimes they drag or directly carry tools or loads.
One of the problems with many tractors and trailers is the amount of space they take to operate and turn. This can be of concern in any situation in which lack of maneuvering space is an issue, as it can be on factory floors, in warehouses, at construction sites, in truck yards, or in boat yards, just to name a few.
In shipyards, for example, it is often desirable to store ships, such as pleasure boats and yachts which have been taken out of the water, as close together as possible. This is because the waterfront real estate on which many boat yards and marinas are located is expensive. But most vehicles capable of pulling boat trailers, such as pickup trucks or truck tractor are highway vehicles which are normally at least twelve or fifteen feet long. Not only are such vehicles relatively large, which makes it difficult for them to fit into narrow spaces, but also they cannot turn sharply, further increasing the amount of space they require in which to operate. Most boat trailers are also difficult to maneuver, further decreasing the number of boats which can be stored in a given amount of real estate.
It is common for tractors used with boat trailers to help launch and retrieve boats by backing the boat trailers down a launching ramp which descends to, and below, the water level. One of the problems in such launchings and retrievals is that the trailer often has to be placed sufficiently deeply in the water that its tractor must get wet, which can damage the tractor's parts.
Many devices carried or pulled by tractor's require hydraulic or electric power. For example, many boat trailers have hydraulic arms, to lift up, or let down the hull of a boat they are carrying. Usually such trailers contain their own hydraulic pump and a motor for powering it. This equipment adds to the cost of boat trailers, and it can be damaged when such trailers are placed below the water line in the launching of a boat.
It is not uncommon for boat yards and other businesses to want maneuverable tractors and trailers which can be used inside as well as outside. For example, many people in the boat industry often take boats to in-door boat shows. When this is done the boats have to be moved in crowded enclosed spaces, where normal gasoline powered tractors would create offensive pollution.
Often it is desirable to pull or carry cargoes or equipment on locations where traction is an issue. For example such cargoes or equipment often has to be transported in dirt, sand, or mud. Many vehicles are not equipped for transport on such terrains.
Unfortunately tractors, particularly ones designed for pushing and pulling heaving loads, are relatively expensive. Therefore it is desirable increase the possible uses of such vehicles to better justify their worth.